[Pw_forum] Example7

Amit Kumar amit76.india at gmail.com
Tue Mar 6 07:29:00 CET 2007

```   Respected Users,

I'm very much confused with the Electron-phonon output of Example 7.

1 .  KPOINT  16 16 16 for scf.fit    and   2 2 2 for scf calculation.

Gaussian Broadening:   0.090 Ry, ngauss=   0
DOS =  2.674745 states/spin/Ry/Unit Cell at Ef=  8.266810 eV
lambda( 1)=  0.1373   gamma=   15.97 GHz
lambda( 2)=  0.1116   gamma=   12.97 GHz
lambda( 3)=  0.0504   gamma=    6.93 GHz

Gaussian Broadening:   0.10 Ry, ngauss=   0
DOS =  2.674314 states/spin/Ry/Unit Cell at Ef=  8.266772 eV
lambda( 1)=  0.1403   gamma=   16.32 GHz
lambda( 2)=  0.1132   gamma=   13.16 GHz
lambda( 3)=  0.0520   gamma=    7.15 GHz

2.   KPOINT  16 16 16 for scf.fit    and   8 8 8 for scf calculation.

Gaussian Broadening:   0.090 Ry,       ngauss=   0
DOS =  2.673746 states/spin/Ry/Unit Cell at Ef=  8.271433 eV
lambda( 1)=  0.0828   gamma=    8.96 GHz
lambda( 2)=  0.1720   gamma=   26.90 GHz
lambda( 3)=  0.1742   gamma=   27.24 GHz

Gaussian Broadening:   0.10 Ry, ngauss=   0
DOS =  2.674314 states/spin/Ry/Unit Cell at Ef=  8.266772 eV
lambda( 1)=  0.0831   gamma=    8.99 GHz
lambda( 2)=  0.1721   gamma=   26.93 GHz
lambda( 3)=  0.1740   gamma=   27.22 GHz

So I thought great I got  convergency so easily.
lambda( 2)=  0.1720   gamma=   26.90 GHz
lambda( 3)=  0.1742   gamma=   27.24 GHz

and

lambda( 2)=  0.1721   gamma=   26.93 GHz
lambda( 3)=  0.1740   gamma=   27.22 GHz

Very excellent results.

But. life is not  so simple. Bad luck.
With even  more K points again results start to become worse instead of
being better.

3.   KPOINT  32 32 32  for scf.fit    and   16 16 16  for scf
calculation.

Gaussian Broadening:   0.090 Ry,       ngauss=   0
DOS =  2.675256 states/spin/Ry/Unit Cell at Ef=  8.271367 eV
lambda( 1)=  0.0799   gamma=    9.12 GHz
lambda( 2)=  0.1703   gamma=   28.62 GHz
lambda( 3)=  0.1705   gamma=   28.64 GHz

Gaussian Broadening:   0.10 Ry,       ngauss=   0
DOS =  2.674732 states/spin/Ry/Unit Cell at Ef=  8.266803 eV
lambda( 1)=  0.0799   gamma=    9.12 GHz
lambda( 2)=  0.1686   gamma=   28.32 GHz
lambda( 3)=  0.1687   gamma=   28.34 GHz

4.    KPOINT  64 64 64   for scf.fit    and   32 32 32   for scf
calculation.

Gaussian Broadening:   0.090 Ry,       ngauss=   0
DOS =  2.675273 states/spin/Ry/Unit Cell at Ef=  8.271375 eV
lambda( 1)=  0.0801   gamma=    9.07 GHz
lambda( 2)=  0.1726   gamma=   28.29 GHz
lambda( 3)=  0.1726   gamma=   28.29 GHz

Gaussian Broadening:   0.10 Ry,       ngauss=   0
DOS =  2.674745 states/spin/Ry/Unit Cell at Ef=  8.266810 eV
lambda( 1)=  0.0802   gamma=    9.08 GHz
lambda( 2)=  0.1708   gamma=   27.99 GHz
lambda( 3)=  0.1708   gamma=   27.99 GHz

Would anybody tell me the reason,  Why the case (2)    ( for magic
number
KPOINT  16 16 16 for scf.fit    and   8 8 8 for scf calculation)
is  so kind
to us?????? How far we will go to get the converged value???
Where can we stop????
It's really confusing.